Roentgen discovered X-radiation by the inadvertent exposure of a silver halide photographic element. In 1913 the Eastman Kodak Company introduced its first product specifically intended to be exposed by X-radiation. Silver halide radiographic elements account for the overwhelming majority of medical diagnostic images.
In recent years a number of alternative approaches to medical diagnostic imaging, particularly image acquisition, have become prominent. Medical diagnostic devices such as storage phosphor screens, CAT scanners, magnetic resonance imagers (MRI), and ultrasound imagers allow information to be obtained and stored in digital form. Although digitally stored images can be viewed and manipulated on a cathode ray tube (CRT) monitor, a hard copy of the image is almost always needed.
The most common approach for creating a hard copy of a digitally stored image is to expose a radiation-sensitive silver halide film through a series of laterally offset exposures using a laser, a light emitting diode (LED) or a light bar (a linear series of independently addressable LED's). The image is recreated as a series of laterally offset pixels. Initially the radiation-sensitive silver halide films were essentially the same films used for radiographic imaging, except that finer silver halide grains were substituted to minimize noise (granularity). The advantages of using modified radiographic films to provide a hard copy of the digitally stored image are that medical imaging centers are already equipped to process radiographic films and are familiar with their image characteristics.
A typical film, Kodak Ektascan HN.TM., for creating a hard copy of a digitally stored medical diagnostic image includes an emulsion layer coated on a clear or blue tinted polyester film support. The emulsion layer contains a red-sensitized silver iodobromide (2.5M % I, based on Ag) cubic grain (0.33 .mu.m ECD) emulsion coated at a silver coverage of 30 mg/dm.sup.2. A conventional gelatin overcoat is coated over the emulsion layer. On the back side of the support a pelloid layer containing a red-absorbing antihalation dye is coated. A gelatin interlayer, used as a hardener incorporation site, overlies the pelloid layer, and a gelatin overcoat containing an antistat overlies the interlayer. Developed silver is relied upon to provide the infrared density required to activate processor sensors. No dye is introduced for the purpose of increasing infrared absorption.
It is the prevailing practice to process radiographic films and the film described above in 90 seconds or less. For example, the Kodak X-OMAT 480 RA.TM. rapid access processor employs the following processing cycle:
______________________________________ Development 24 seconds at 35.degree. C. Fixing 20 seconds at 35.degree. C. Washing 20 seconds at 35.degree. C. Drying 20 seconds at 65.degree. C. ______________________________________
with up to 6 seconds being taken up in film transport between processing steps.
A typical developer (hereinafter referred to as Developer A) exhibits the following composition:
______________________________________ Hydroquinone 30 g Phenidone.TM. 1.5 g KOH 21 g NaHCO.sub.3 7.5 g K.sub.2 SO.sub.3 44.2 g Na.sub.2 S.sub.2 O.sub.3 12.6 g NaBr 35.0 g 5-Methylbenzotriazole 0.06 g Glutaraldehyde 4.9 g Water to 1 liter/pH 10.0 ______________________________________
A typical fixer exhibits the following composition:
______________________________________ Sodium thiosulfate, 60% 260.0 g Sodium bisulfite 180.0 g Boric acid 25.0 g Acetic acid 10.0 g Water to 1 liter/pH 3.9-4.5 ______________________________________
Radiographic film processors such as RA 480 are capable of exposing large amounts of film over extended periods of time (e.g., a month or more) before its processing solutions are drained and replaced. Extended use of the processing solutions is made possible by the addition of small amounts of developer and fixer replenishers as each film is processed to compensate for developer and fixer losses by evaporation and film pick up.
Harada et al U.S. Pat. No. 5,260,178 has noted that if the silver halide coating coverage of a radiographic element is quite low, it is impossible for sensors that rely on the attenuation of near infrared sensor beams by silver halide grains to sense the presence of the film in the processor. Hence replenishers are not automatically added to the processing solutions, and the useful life of the processing solutions is markedly decreased. To overcome this problem Harada et al suggested adding to radiographic elements having low silver halide coating coverages an aggregated tricarbocyanine dye having at least two acidic (e.g., sulfonic acid or carboxylic acid) substituents and an absorption peak that is bathochromically shifted by at least 50 nm when aggregated as compared to its absorption in solution. The dye as aggregated in the radiographic film attenuates the infrared sensor beam to provide the necessary signal to turn on the processor. However, once the dye has entered the processing solution (as is insured by the presence of the acidic groups), it is no longer capable of attenuating the infrared sensor beam. Instead developed silver is used to control processor shut off. When the beam of the sensor controlling shut off ceases to be attenuated by developed silver, thereby indicating the film has passed through the processor, the processor is automatically turned off.
Thiaalkylene bisquaternary ammonium salts have been employed for a variety of purposes in silver halide photography. They are, for example, thioethers and hence capable of acting as grain ripening agents. They have been used in fixers, as illustrated by Schmittou EPO 0 569 008, Watanabe EPO 0 458 277 and Okazaki U.S. Pat. No. 4,960,683. Ishihara et al U.S. Pat. No. 3,827,886 discloses their utility as fog reducing agents in combination with 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene.